The subject matter disclosed herein relates to rotor blade spar formation with automated fiber placement and, more particularly, to a method of rotor blade spar formation with automated fiber placement and pre-impregnated tows.
A rotor blade spar is a primary structural element of a helicopter rotor blade assembly inasmuch as its primary function is to transfer combined flapwise, edgewise, torsional and centrifugal loads to/from a central torque drive hub member. Typically, leading edge and trailing edge assemblies envelop the spar to yield a desired airfoil contour. The spar typically extends along the length of the rotor blade and is mounted at its inboard end to the hub member.
Fiber reinforced resin matrix composite materials are employed in the formation of the spar due to their tendencies to provide advantageous strength to weight ratios. Despite the inherent weight and strength advantages of these materials, however, widespread use of fiber reinforced resin matrix composite materials has been impeded by high costs and associated fabrication methods being difficult to execute.
As an example, conventional methods for manufacturing composite spars include filament winding and prepreg lay-up of composite materials. Although effective, these processes are relatively time and labor intensive. The prepreg lay-up process is primarily performed by hand and prepregs have little structural rigidity in their uncured state. The prepregs are hand-stacked and interleaved upon an inflatable mandrel assembly. The lay-up is then transferred into a matched metal mold and autoclave oven cured while the mandrel assembly is inflated to form the finished composite spar. Moreover, prepreg sheets are relatively expensive and require meticulous storage and handling processes which further increase manufacturing expense.